The class never changed, it stayed with book. But some packages of the KOMA-bundle have been included, some commands have been added that resemble KOMA-commands (but do far less of the compicated stuff).

Edit: I should note that \abovechapterskip is defined since versioin 2.4 of the template, dating november 2016.

The smart way: Calm down and take a deep breath, read posts and provided links attentively, try to understand and ask if necessary.

First of all I would like to thank both of you for your kind and sincere suggestion. But, I have updated the .cls file only after changing the name of the class file to "MastersDoctoralThesis_UoM."

Regarding, the last request of removing un-necessary space above contents, list of tables, list of figures and chapter is not yet solved. Please find the small piece of code below and help me out in this regard.

This still is not a minimal working example, but nevermind. How should have anyone guessed, that you are using package titlesec? What you are looking for is \titlespacing*{\chapter}{0cm}{-\topskip}{2\baselineskip}[0pt]

With an unmodified and up to date version of the template, this can be done with just three (or four) lines of code.

One more clarification related to heading, we need to add horizontal line below the table of contents, list of figure, and list of tables just similar to chapter title. Please help me out in this regard. The following is the sample code: